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15 N methodology and calculation Calculation of the N recovery For each selected compartment (peat, N mineral, microbial biomass, etc.), the recovery from the N input is calculated as : % R = (E i /E o ) * (N i /a) * 100 With : N i = N stock of the compartment i a = N mass of the input (litter at the start of the experiment) E i = isotopic excess of the compartment i E o = isotopic excess of the input E i /E o corresponds to the N part coming from the tracer. This is equal to the Ndff = Nitrogen derived from fertilizer (Powlson & Barraclough 1993, Guiraud & Boniface 1987)

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Fate of N from the litter Concluding remarks Fate of N from liter : as the N decreases from litter,  it increases in the peat but in which compartments : - probably microbial biomass - mineral N ?? Signicant decay through time (2 months)  mineralization takes place at this time level (shown by the decreasing of N mass in the litter, not presented here)

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Fate of litter : what about C ? 13 C in from the harvesting of gaz emissions : OK 13 C in the litter and the peat : OK but I need the value of natural abundance value to calculate the recovery in litter through time) In addition, we ‘ve got samples at 6 months …